As you may have read in previous posts, I think the best approach is to prepare a full manuscript, but then to preach without notes. The full manuscript allows you to sculpt and craft the language carefully in order to be precise and effective. This can be overdone and end up feeling like a contrived performance, or underdone and end up feeling like a rambling grasping for the right words. But the main rule to remember when writing a manuscript is that you are trying to write for the ear, not the eye. Most other rules can and maybe should be broken.
For example, David Buttrick helpfully suggests that a single move in a sermon (think “point”) may last 3-4 minutes, but since it has inherent unity, it should be manuscripted in a single paragraph. If the stages of development within a move are manuscripted as separate paragraphs, then the move will tend to fall apart. First sentences in paragraphs tend to break the flow of an idea as it is still forming. Perhaps this reflects the nature of oral communication. When speaking to a group, it takes longer for a thought to form in the group consciousness. Hence longer paragraphs. (See Buttrick’s Homiletic, p50)
Let me quickly incorporate that suggestion in a simple three-level approach to writing for the ear:
On a micro level, sermon manuscripts can break rules of sentence structure. You must write as you speak. Yes. Sometimes incomplete sentences.
On a mid level (is that the right term?), sermon manuscripts will include more repetition that normal written prose. Your manuscript will show evidence of going over the same concept. Repeating, or even better, restating what you’ve just written. You wouldn’t do this in written English, but you’re writing for the ear and that requires repetition and restatement. Saying the same thing again in different terms. Giving hearers one more opportunity to catch what you’ve been saying.
And on a macro level, sermon manuscripts should reflect the unity of the sub-parts in a sermon. So a movement, or point, should cohere. Using bigger paragraphs may help achieve that inner unity.
Biblical Preaching 
Thank you for this information about writing manuscripts. I started preaching several years before I had a preaching class and then my first class required only one manuscript, but the focus was on outlines. I’ve used manuscripts, but always felt stilted in doing so. I’ve gone back to outlines, but still desire to use manuscripts. My sense is that my preparation will be more complete and that I will be able to preach without any notes if I do so. Perhaps these guidelines will be keys to a successful endeavor of writing manuscripts.